Sealing of semiconductor devices is carried out with the use of a transfer-molding with a metal mold, potting with a liquid sealing resin, or screen-printing with a liquid sealing resin. The recent trend towards miniaturization of semiconductor devices demands that electronic devices be smaller in size, thinner in thickness, and allow resin sealing of packages as thin as 500 μm or thinner.
If a transfer-molding is employed in resin sealing of thin packages, the thickness of the sealing resin could be precisely controlled, whereas there are problems that vertical displacements of semiconductor chips occur in a flow of a liquid sealing resin, or breakage of wires and contact between the wires occur because of deformations of bonding wires connected to semiconductor chips under the effect of pressure in the flow of the liquid sealing resin.
On the other hand, although potting or screen-printing with a liquid sealing resin to some extent protects the bonding wires from breakage and mutual contact, these methods make accurate control of sealing-resin coatings more difficult and can easily lead to formation of voids.
It was proposed to solve the above problems and to manufacture a resin-sealed semiconductor device by placing an unsealed semiconductor device into a mold, filling spaces between the semiconductor device and the mold with a moldable resin, and curing the resin by using compression-molding (see Japanese Laid-Open Patent Application Publication (Kokai) (hereinafter referred to as “Kokai”) Hei 8-244064, Kokai Hei 11-77733, and Kokai 2000-277551).
However, due to thinning of semiconductor chips that occurs with miniaturization of semiconductor elements, these methods increase warping of the semiconductor chips and printed-circuit boards and may lead to damaging of semiconductor devices and to worsening of their performance characteristics.
It is an object of the present invention to provide a method for efficient manufacturing of sealed semiconductor devices that prevent formation of voids in the sealing material and reduce warping of semiconductor chips and printed-circuit boards, which in case of sealing with a curable liquid silicone composition, can be sealed quickly and with adequate moldability. It is another object to provide sealed semiconductor devices with the aforementioned properties.